The present invention relates to a process for producing alkali metal siliconates and more specifically the present invention relates to an improved process for preparing alkali metal siliconates, by first alkoxylating a major portion of the chlorine groups in the chlorosiliane reactant.
Silicone resins, and silicone resin solutions, are well-known as environmental protecting agents for masonry.
Briefly, silicone resins, as is well-known, and silicone materials, as is well-known, have improved resistance to the elements and the ultra-violet rays of sunlight as well as being eminently water-repellant.
Accordingly, it was early known in the industry to prepare organic solvent, silicone resin solutions at a solid concentration of 1 to 10 percent by weight and apply any such silicone resin solutions to masonry so that the masonry would be further water repellant than was the case without such a protective coating.
However, such silicone resin organic solvent solutions were not always suitable in protecting masonry surfaces that were not very porous. Accordingly, in the case of marble and high calcium-carbonate content masonry surfaces, the use of such silicone materials did not have as many advantages as with other types of masonry surfaces. With the silicone organic solvent solutions that were applied to protect such surfaces, the silicone did not become absorbed as much as would be desired on the surface of the masonry and as a result it would tend to stay completely on the surface of the masonry.
One disadvantage of such silicone resin solution when applied to masonry surfaces with a small amount of porosity was that the silicone resin that tended to stay completely on the surface of the masonry, tended to pick up dirt which is a property of some silicone water repellants. Accordingly, there was a tendency when such non-porous masonry surface were coated with such silicone resin solutions, that such masonry surfaces would be susceptible to dirt pick up, and as a result would be susceptible to discoloration and also a greater tendency to be washed away.
Accordingly, for such non-porous, or minor porosity masonry surfaces, it was highly desirable to utilize a different type of silicone material to coat such masonry surfaces. In addition, the prior art silicone resins which were applied in the form of organic solvent solutions would unduly increase the cost of such coating solutions, as well as possibly presenting some environmental problems. In addition the prior silicone materials would not cure completely thus making them susceptible to being washed off the surface. For these reasons, it was desirable to have a silicone material which could be utilized to coat masonry surfaces which could be utilized to coat masonry surfaces which could be utilized in an aqueous solution. It was also highly desirable that such silicone material, which could be applied in an aqueous solution, be able to migrate even into minor porosity masonry surfaces and cure completely such that the coating on such masonry surfaces would not have excessive dirt pickup from the atmosphere by the silicone material and such that the silicone material would provide the proper protection to the masonry surface against the elements.
Accordingly, for this purpose and for the coating of such masonry material and fulfilling the above objects there was devised alkali metal siliconates which were formulated in aqueous solutions for the purpose of coating masonry surfaces, with the foregoing advantages mentioned previously. However, such alkali metal siliconates had one disadvantage. In their preparation, which normally required the addition of a chlorosilane and more speficially, methyltrichlorosilane to water and then subsequently to an aqueous sodium hydroxide or potassium hydroxide solution, with or without the presence of an alcohol, there resulted the formation of a gel, which gel was very difficult to purify and which gel was very difficult to re-dissolve aqueous alkali solutions so as to provide the appropriate aqueous solution of the siliconate for application to masonry surfaces.
Some of the prior art U.S. patents in preparation of such siliconate materials that should be mentioned are, for instance:
______________________________________ Hyde et al 2,438,055 Elliott et al 2,507,200 MacMullen 2,587,636 Barry 2,469,625 Bidaud et al 2,567,315 Biefeld 2,392,805 Brick 2,574,168 Cruz, Jr. 2,519,232 Currie 2,523,281 Dennett 2,588,365 Dennett 2,588,366 Hyde 2,439,689 Krieble et al 2,441,422 Elliott et al 2,441,423 Norton 2,386,259 Norton 2,412,470 Patnode 2,306,222 Pierce 2,500,770 Rasmussen 2,612,482 Safford 2,510,661 Slayter 2,604,688 Thayer 2,474,704 Roedel 3,846,358 Agnew 2,504,484 ______________________________________
With respect to the foregoing Hyde et al Pat. No. 2,438,005 it should be noted that the chlorosilane or mono-organo trichlorosilane material is reacted with an alkali metal hydroxide in the presence of water and an alcohol in a single phase system from which complex salts containing water of crystalization, crystallized out. This method, while not specifically speaking of a gel, notes the formation of solid crystaline materials which precipate out, which not only lower the yield in the process but require subsequent purification techniques. At any rate, it was highly desirable to provide for a process of producing alkali metal siliconates in which the reactants would remain in solution and would remain in a liquid stage throughout the entire process up to the formation of the final product, such that the final product, the alkali metal siliconate, was always in solution. Such a process would obviate the need of purification and handling of a gel as was the case with the prior art processes and would eliminate the need for purification or subsequent purification steps in the removal of unwanted salts which not only would involve additional purification techniques but in addition would lower the yield from the foregoing process.
Accordingly, it is one object of the present invention to provide for an improved process for producing alkali metal siliconates wherein in the process a gel is not formed.
It is an additional object of the present invention to provide for an improved process for producing an alkali metal siliconate in which complex salts do not precipitate out and are not formed.
It is yet an additional object of the present invention to provide for an improved and more efficient process for producing alkali metal siliconates.
It is still an additional object of the present invention to provide for an improved process for preparing an alkali metal siliconate aqueous solution which is highly suitable for coating masonry surfaces.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.